Diesel engines in certain motor vehicles often use a starting aid or aids, particularly when engine starting is attempted in cold weather. A starting aid is employed to provide heating that will assure combustion of injected diesel fuel by compression ignition when the engine is cranked.
One type of cold start aid is commonly referred to as a block heater. A typical block heater is an accessory device that is mounted on an engine for delivering heat to the engine when an electric cord running from the device is plugged into a nearby electrical outlet. The use of household or commercial electric power, rather than the vehicle's battery or battery bank, can deliver more heat, and without battery drain. When a vehicle has been parked and its engine shut off, a block heater can be used to maintain engine heat in cold weather. Alternatively it can be used to raise the temperature of a cold-soaked engine prior to cranking.
Glow plugs are another type of cold start aid. A glow plug starting aid system typically comprises one or more glow plugs associated with each combustion chamber, and some form of controller or control system that controls the delivery of electric current to the glow plugs from the vehicle battery or battery bank. Glow plugs typically operate only after the ignition switch has been turned on, and only for a limited amount of time.
A glow plug lamp in an instrument panel typically serves as a wait-to-start indicator to inform the driver that the glow plugs have been turned on and that he should wait to crank the engine to allow the glow plugs to be effective. The glow plugs may continue to be energized for some amount of time after the engine has been cranked and commences running under its own power. A glow plug is intended to create a hot spot in a combustion chamber whereas a block heater is typically installed in a block cooling jacket to deliver heat to engine coolant.
When an engine that has been heated by a block heater is to be started in cold weather, the temperatures of the coolant and of surfaces in contact with the coolant are generally significantly higher than those at other locations, such as in the crankcase and oil galleries.
Another device that can aid engine cold-start is a manifold air intake heater. Such a heater, when electrically energized, heats charge air in the engine intake system before entering the combustion chambers. Control of heating by an air heater may occur in coordination with, or independently of, glow plug control.
The fuel injection systems of certain diesel engines use hydraulic fluid under pressure to force fuel into engine combustion chambers. The hydraulic fluid, typically engine oil, is supplied to a respective fuel injector at each engine cylinder. When a valve mechanism of a fuel injector is operated by an electric signal from an engine control system to inject fuel into the respective cylinder, the hydraulic fluid is allowed to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber. The pressure of the fluid, referred to as injection control pressure, or simply ICP, is also controlled by the engine control system. Because fluid viscosity is affected by temperature, it is appropriate that the control system take temperature into account when setting ICP.
Because block heaters typically elevate engine coolant temperature more significantly than engine oil temperature, a control strategy that sets certain starting parameters, intake air heater on-time and ICP for example, based only on engine coolant temperature might set them to values that are less than optimal for actual temperatures elsewhere in the engine and the prevailing ambient temperature. A block heater that has been heating a cold-soaked engine may elevate engine coolant temperature on average 45° F. higher than engine oil temperature before the engine is cranked, and if the control system sets ICP based on a temperature that is significantly different from one that accurately reflects the viscosity of the lower temperature engine oil, ICP may not be set to an optimal pressure.
In a similar way, when intake air heating and/or glow plug heating are used after block heating, their operation may not be optimized because of temperature differentials created by use of the block heater.
Heretofore, engine coolant temperature data was considered suitable by itself for engine temperature data needed by the engine control system to control temperature-dependent variables that affect the starting procedure for a cold-soaked engine. Those variables include ICP and control parameters for an intake air heater.